By capturing a change in capacitance generated by a user performing a touch operation, a touch panel recognizes the touch operation and outputs a signal corresponding to content of the operation (refer to Japanese Patent Application Laid-Open Publication No. 2014-16924, for example).
Such a touch panel is applied to a remote control that is disposed on a wall of a room or the like for controlling an air conditioner, for example.
DC power generated from a commercial AC power source is supplied to the above-mentioned touch panel for operation.
The capacitance of the touch panel is converted into a voltage signal, and a control circuit determines whether a touch operation has occurred by capturing the change of the capacitance by A/D-converting and sampling the voltage signal.
In this case, a ground potential of a circuit board is preferably equal to an earth potential, which is a potential reference of the user who performs the touch operation.
However, an area of a ground pattern of the circuit board cannot be sufficiently secured when the size of the touch panel device becomes compact, therefore impedance rises and the device is influenced by noise, and there may be a case where the ground potential is different from the earth potential.
When the control circuit A/D-converts the voltage signal under such a situation, there is a possibility that a variation occurs in the value of the A/D-converted data and the circuit may therefore erroneously detect the presence of a touch operation.